#6
import math

ab=eval(input())
cd=eval(input())
ad = ab/2
oa = (ad**2+cd**2)/(2*cd)
aob =2 * math.asin(ad/oa)
sector = aob / (2*math.pi) * math.pi * oa ** 2
triangle = 0.5*oa**2*math.sin(aob)
arch = sector - triangle
print(f"{arch:.2f}")